After changing boot location from HD1 to HD2 to upgrade to 11.4.0 , my f5 LTM 2000 is not coming up.....

You should connect to the AOM via SSH or to the serial console to see what is happening. I do not think there is much else that can be done. What output is there on the LCD?

Keep in mind that it could be down for an extended period of time while it flashes hardware components such as the BIOS, FPGAs, ASICs and so on.